A conventionally known manufacturing line that performs a photolithographic process on a semiconductor device, liquid crystal display element or the like comprises, as shown in FIG. 6, a plurality of steppers 1 and one host computer 2 for controlling the plurality of steppers 1, the steppers and the host computer being connected to each other via a communication line 3.
In such a manufacturing line, each stepper 1 is adapted to perform an exposure process under the control of the host computer 2. First, an operator manipulates an online terminal for the host computer to obtain a process recipe from the host computer 2. Then, after a reticle is set in a reticle library capable of housing a plurality of reticles, according to the process recipe, the operator gives the stepper 1 an instruction to start the process via the terminal and the host computer. Thereby, after automatic replacement of the reticle, the stepper 1 transports a plurality of wafers housed in a predetermined cassette onto an exposure stage one by one, transfers a pattern formed on the reticle to the wafer, and places the wafer having the pattern transferred thereto into the cassette.
The conventional stepper 1 requires the operator to stop transportation of the wafers and perform the terminal manipulation or the like every time exposure of all the wafers processed according to the same process recipe is finished.
Therefore, in the case where a large number of wafers are subject to exposure in the same process recipe as in the case of producing the memory, which was a mainstream of the conventional semiconductor manufacturing industry, that is, in the case where limited kinds of products are to be provided in large quantity, the stepper 1 can perform exposure on wafers housed in different cassettes sequentially without stopping transportation of the wafers, and thus, the availability is high.
However, in recent years, products that can be mass-produced, such as memories, tend to decrease in price, and thus, attentions of many semiconductor manufacturers has been shifted to manufacture of high-value-added custom products. Since the above-described conventional stepper 1 requires manipulation by the operator for a following process every time the process recipe is changed, a time of waiting for the operator manipulation is required. Thus, the stepper 1 is stopped until the operator starts the manipulation for the following process, and thus, there is a possibility that the availability of the stepper 1 is reduced. In particular, in the case where the number of wafers that is processed according to the same process recipe is small (in the case where many kinds of products are to be provided in small quantity), such as in the case of manufacture of a custom product, there is a possibility that the availability of the stepper 1 and thus the throughput thereof are significantly reduced.
Thus, in recent years, there has been developed an arrangement in which a process recipe for a second group of wafers is loaded into the stepper 1 before exposure of a first group of wafers is completed. For example, a known stepper 1 of this type incorporates cassettes each housing wafers processed according to a same process recipe to be adapted for manufacture of many kinds of products in small quantity, obtains from the host computer 2 a process recipe for wafers housed in another cassette before exposure of all the wafers housed in one cassette is completed, and after exposure of the wafers is completed, replaces the reticle with a new one according to the new process recipe and then, starts transportation of the wafers housed in said another cassette.
However, according to the latter conventional technique, since the recipe for the following group of wafers is transmitted to the stepper 1 from the host computer during exposure of the wafers, even if the number of wafers processed according to a same process recipe is small, the availability of the stepper 1 can be prevented from being reduced. However, since transportation of wafers is stopped every time exposure of all the wafers housed in one cassette is completed, for example, even if the wafers processed according to the same process recipe cannot be housed in one cassette and is separately housed in two or three cassettes, transportation of the wafers is stopped every time exposure of the wafers in one cassette is completed. Thus, there is a problem in that the availability of the stepper 1 and thus the throughput thereof is low.
Such problems are not specific to the stepper 1 that performs exposure, and are also found in semiconductor manufacturing apparatus that performs other processes.
The present invention has been devised to solve the problems described above found in the prior art. An object of the invention is to provide a control system for a semiconductor manufacturing apparatus that allows reduction of a stop time of transportation of wafers which occurs when one semiconductor manufacturing apparatus manufactures many kinds of products.